The present invention relates to a plasma processing apparatus and a plasma processing method; and, more particularly, the invention relates to a plasma processing apparatus and a plasma processing method suitable for processing a specimen, such as etching a specimen using a high density plasma.
In a conventional plasma processing apparatus, as described, for example, in Kanno, T., Semiconductor Plasma Processing Technology, Sangyou-Tosho Company (1980), page 139, using a microwave plasma processing apparatus, which has a quartz discharge chamber in a waveguide transmitting a microwave, plasma is generated in the discharge chamber by action of an outer magnetic field generated by a coil arranged outside of the discharge chamber and a microwave electric field. Thereby, processing, such as etching of a surface of a semiconductor wafer, can be performed using the plasma.
For a processing chamber in such a microwave etching apparatus, a non-magnetic and conductive material used as the waveguide is necessary to guide the microwave energy and to introduce the outer magnetic field in the processing chamber. Therefore, a metal, such as aluminum (Al) or a stainless steel (SUS), is commonly used for the wall material of the processing chamber.
However, a metal, such as a stainless steel or the like, composing the wall surface of the processing chamber, becomes worn and dispersed by the plasma, and the heavy weight metals contained in the material become a contamination source.
A technology is disclosed in Japanese Patent Application Laid-Open No. 4-229619 (1992) where a conductive coating film capable of protecting a metallic surface from chemical corrosion by a reaction gas used in a processing chamber is formed on the metallic inner surface. In accordance with this technology, a protective film is formed on the metallic inner wall surface of the processing chamber through coating, since the metallic inner wall surface may be corroded when plasma etching is performed by using a halogen gas, such as chlorine, as the processing gas. Aluminum is used as the material for the processing chamber, and TiN, InSn, SiC, TiC, TaC or the like is used for the coating material. The thickness of the coating film is 0.2 .mu.m to 1 .mu.m.
Further, a dry etching apparatus having opposed electrodes inside a chamber is disclosed in Japanese Patent Application Laid-Open No. 63-138737 (1988), wherein the inside surface of the chamber is covered with an insulator material detachable from the chamber in order to keep a contaminated inner surface of the chamber clean. As the insulator material, there is used alumite, alumina thermal spraying, teflon, ceramic or the like.
The above conventional technology disclosed in Japanese Patent Application Laid-Open No. 4-229619 (1992) can protect the metallic surface from chemical corrosion due to the reaction gas used in the processing chamber. However, as for the typical condition of the plasma etching process, it is clear that the temperature during plasma processing is limited to a relatively low temperature range of approximately 10.degree. C. to approximately 70.degree. C. The reason why this temperature limitation is set seems to be that cracks may occur in the coating film on the aluminum surface due to the thermal expansion of the aluminum if the temperature of the aluminum composing the process chamber rises above 100.degree. C. during plasma processing. In order to avoid the occurrence of cracks, the thickness of the coating film must be reduced. However, if the thickness of the film is reduced, the coating film cannot perform its function, since it will be corroded out in a short time by the reaction gas generated during plasma etching. For example, data according to an experiment conducted by the inventors shows that an SiC film is worn off at a speed of approximately 0.05 .mu.m/minute during etching. This means that a coating film having a thickness of 0.2 .mu.m to 1 .mu.m is damaged and eliminated in several hours, that is, during a time when several hundreds of specimens have been processed. As a result, the metallic surface of the inner wall of the process chamber is exposed to the plasma and worn off by the plasma or has its quality altered due to chemical reaction. The worn-off metal becomes a heavy metal contamination source and the quality-altered metallic wall degrades the characteristic of the process chamber.
On the other hand, in the invention disclosed in Japanese Patent Application Laid-Open No. 63-138737 (1988), a contaminated isolator member is dismounted from a chamber and cleaned, and then re-mounted in the chamber to be used again. However, in a system where an insulator member is mounted onto the inner surface of a chamber, there is a problem in that the plasma processing characteristic largely fluctuates because the temperature of the mounted insulator member fluctuates during plasma processing.